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[quote=epicsteve ]
Also my testing with just the rear brake indicated that skidding to a stop took noticeably longer than trying to not skid. With the rear locked the bike didn't seem to be slowing much at all.
Which is why ABS systems (yes, a tautology) are designed the way they are. Maximum retardation is prior to the wheel skidding.
[quote=epicsteve ]I've got visitors staying at the moment who have brought a couple of cheapo mountain bikes (not quite bike shaped objects but not far off - they have V-brakes with non cartridge pads although they do seem to be set-up quite well) so am tempted to try on one of those. I'd love to try on a Boris bike as well, as their brakes aren't great.
That would be interesting - please do if you get the chance! I don't think you could be charged with wilful neglect riding a bike with fresh from Halfords brakes, which is what we're talking about here.
Just as an aside, trying to stop quickly while in full flight on a TT bike is one of the scariest things you can do.
One of mine brakes well and the other one not so much with the difference seeming to be more about the levers than anything else. The crap one has little Vision levers that are very aero but feel like trying to pull a razor blade - not nice. They're being replaced by some rather nicer feeling ones that just arrived today!
It's not the grippiness though, but that the geometry limits the ultimate stopping distance - no matter how good your brakes are and how much traction you have, at some point you'll just go over the bars. It should in theory be possible to stop just as fast without using the back brake at all as the rear tyre will have no weight on it in a maximum braking stop.
Eh? the amount of grip available is huge factor in how quickly you can stop - you cannot dismiss that. You cannot take any single factor and claim that governs the limit - it is all of the combined factors that will determine stopping distance.
And what we talking about here is minimum possible stopping distance - what we should be talking about is maximum reasonable stopping distance.
Which is why ABS systems (yes, a tautology) are designed the way they are. Maximum retardation is prior to the wheel skidding.
Indeed. The reason I tried it as we've heard from the Gods of fixie about how physics doesn't apply to them and skid stops are wonderfully effective. I'd assumed it was total bollocks but have now proved it to myself. On a properly wet road I suspect with a heavy git like me riding the bike the stopping distance for a skid stop would be measured in miles not metres. And that's assuming that you can skid stop effectively on a short wheelbase, high geared track bike - which is also open to dispute.
[quote=sargey2003 ]Eh? the amount of grip available is huge factor in how quickly you can stop - you cannot dismiss that. You cannot take any single factor and claim that governs the limit - it is all of the combined factors that will determine stopping distance.
It is, but once you have enough grip more doesn't help, because if you try and brake at more than 0.5g you'll just pitch yourself over the bars. Ultimately stopping on a bicycle is limited by the geometry because the CofG is quite high and quite far forwards - the real world braking available from a standard brake and from a normal tyre on tarmac is sufficient to go over the bars.
There might be brakes and tyres which result in longer stopping distances (Halfords specials, relying on hop skidding a fixie), but the minimum stopping distance is limited by that.
That would be interesting - please do if you get the chance! I don't think you could be charged with wilful neglect riding a bike with fresh from Halfords brakes, which is what we're talking about here.
There are two reasons I haven't tried using one of my visitors bikes:
1) I'd need to fit a Garmin mount temporarily (ok - that'd take me about a minute!)
2) I can't quite get up the courage to ask if I can borrow one of their bikes a I need a sh1tter for some brake test comparisons!
[quote=epicsteve ]The reason I tried it as we've heard from the Gods of fixie about how physics doesn't apply to them and skid stops are wonderfully effective.
I guessed that might be the case - thanks for checking for us 😆
It is, but once you have enough grip more doesn't help, because if you try and brake at more than 0.5g you'll just pitch yourself over the bars. Ultimately stopping on a bicycle is limited by the geometry because the CofG is quite high and quite far forwards - the real world braking available from a standard brake and from a normal tyre on tarmac is sufficient to go over the bars.
Thinking about it I should probably have fitted my VIRB when testing as it has some kind of G-meter. I'm bored of the testing now though, plus if my neighbours were watching they probably already think I'm mental!
I knew that'd come up, which is why I repeated the test on a more "normal" road bike with rim brakes - with very similar results to the disc braked mountain bike.
You were still using relatively 'high end' kit: Shimano 105 brakes are not what I would consider to be the baseline for minimum braking performance.
Anyway while the distances themselves are certainly open to debate what was a lot more convincing was that it took me twice as long to stop with just a rear brake (and a rear brake that I'm certain was a lot more effective than braking with just the fixed wheel on that track bike would be).
It's not just a question of how much a front brake reduces braking distance compared with leg braking on its own. It's also a question of being able to say (beyond a reasonable doubt?) that the bike that was ridden, if fitted with the legal minimum efficient front brake, would have enabled the cyclist to stop before the colllision, i.e. within 6.85m.
From what I have read, it seems that the speed of the collision was not decisive, it was the fact that she was knocked over and her head struck the road or kerb badly.
Your measurements are very close to that 6.85m distance: factor in potential error in the Garmin and other variables, and it starts to looks like the defence could make a very strong case that it could not be said with confidence that a front brake would have made the difference in the outcome.
[quote=slowster ]
Your measurements are very close to that 6.85m distance: factor in potential error in the Garmin and other variables, and it starts to looks like the defence could make a very strong case that it could not be said with confidence that a front brake would have made the difference in the outcome.
All these measurements are, however, quantifying how much space is required to come to a full stop. Even slowing could/would have reduced the seriousness of the impact and injury
I understand your point of view slowster and personally I wouldn't be surprised if he got off with manslaughter. You might have made a case for the "wanton and furious" charge being proven though i.e. not being able to slow effectively might not be viewed as decisive as a factor in her dying, but could it could be accepted as a factor in her being injured.
[quote=slowster ]Your measurements are very close to that 6.85m distance: factor in potential error in the Garmin and other variables, and it starts to looks like the defence could make a very strong case that it could not be said with confidence that a front brake would have made the difference in the outcome.
Am I being too cynical to wonder if the reason they haven't attacked the "expert" figures is that they know they're bollox and that this gives them grounds for appeal (on the basis of unreliable evidence)?
[quote=scotroutes ]All these measurements are, however, quantifying how much space is required to come to a full stop. Even slowing could/would have reduced the seriousness of the impact and injury
But as he also pointed out, the severity of impact may not have been a significant factor in the death.
I don't think the defence are arguing this, which is why it hasn't come up - closing speeches today though apparently, will be interesting to hear what the defence barrister says.
Your measurements are very close to that 6.85m distance: factor in potential error in the Garmin and other variables, and it starts to looks like the defence could make a very strong case that it could not be said with confidence that a front brake would have made the difference in the outcome.
Based on my limited and unscientific testing I'm pretty convinced that had I been on the road bike with the hydro's I'd have comfortably stopped in time (I did the very first test on that bike and it was well within 6.85m) but with the others and using both brakes it'd have been close, although I'd have been going pretty slow if an impact took place. With the back brake only, even on the bike with the best braking performance, I'd have been travelling much, much quicker at the point of impact (although I couldn't tell you what speed I was doing at that point as I didn't look).
Am I being too cynical to wonder if the reason they haven't attacked the "expert" figures is that they know they're bollox and that this gives them grounds for appeal (on the basis of unreliable evidence)?
More likely it's dangerous to allow that to become the focus of the defence because if they do he's going to jail for sure.
Just as a quick note that stopping distance calculator linked to earlier is bollocks as it doesn't take account of geometry
Just as a quick note that stopping distance calculator linked to earlier is bollocks as it doesn't take account of geometry
I'm glad to hear that it wasn't just me being shit at braking then!
[quote=thecaptain ]Just as a quick note that stopping distance calculator linked to earlier is bollocks as it doesn't take account of geometry
I did mention it earlier in similarly glowing terms, but thanks for the confirmation 😉 http://singletrackworld.com/forum/topic/charged-with-manslaughter-riding-a-fixie/page/12#post-8662716
As I've mentioned a few times, this is also why the reported 3m from 18mph is a load of bollocks, and you don't need to do any testing to prove that (though I suspect most juries are probably more comfortable with tests that equations and diagrams).
One point about brakes.
He appears to have been swerving, so even if he had the finest brakes he wouldn't have been able to use them to much effect.
But then if he had decent brakes maybe he would not have needed to swerve...
The CTC/Cycling UK thread on this contains some interesting information [url= https://forum.cyclinguk.org/viewtopic.php?f=7&p=1156270#p1156268 ]here[/url] regarding the stopping distances, from [url= https://twitter.com/search?l=&q=%23oldbailey%20OR%20%23cyclist%20from%3AByDanSales&src=typd&lang=en-gb ]a Sun journalist's Twitter account[/url],
In short, it seems the 3m stopping distance measured for a MTB must have been based on a lower speed than 18mph, and can only be related to the stopping distance of the defendant's bike at the same speed (whatever that speed was) which was measured to be 12m. Tests performed using the defendant's bike at 17mph (i.e. close to the speed estimated in the accident) resulted in stopping distances of up to 21.3m.
Obviously this is only a very limited second hand extract of the evidence presented in court, and the defence must have had the full report detailing the various testing, presumably including the protocols, well in advance of the trial, and could/would have submitted it to an expert of their own for review.
21.3m for that track bike from 17 or 18mph is believable IMHO and would mean it was about 3 times worse than my road bike with 2 brakes, as opposed to about 2 times worse with a proper rear brake.
Not a chance of 3m from 18mph though - even with my disc braked road bike. Stopping in under 6m on that had the back wheel well off the ground as it was.
don't forget about reaction time recent article suggesting those shown in the Highway Code probably not correct, too short
Those braking figures are plausible if that is the case - working from 21.3m at 17mph, and 12m at the other test speed, the speed for the other tests was 12.75mph (exactly 3/4 of the 17).
I'm not quite sure why they used different speeds for the comparison test - it seems a failure of evidence right there, I can only think there was some deliberate attempt to bamboozle the jury by making them think he could have stopped much quicker than he did. Maybe I'm being too cynical here, but as discussed already the stopping distances at the speed he was reported as going are uncomfortably (for the prosecution) close to the space he had to brake in, hence in order to avoid the collision simply by braking (on a front brake equipped bike) he'd have had to make a perfect stop, difficult in a stressful situation.
Anyway that makes the deceleration for the MTB 0.55g which is feasible.
That then gives the stopping distance of the MTB as 5.3m at 17mph, 6.0m at 18mph.
Though according to that twitter, the stopping distance for the front brake equipped fixie (a road legal bike and the correct comparison) was 3.2m. Once more I'm tempted to think that the only reason for the prosecution including the MTB in the testing is to imply that he could stop quicker, when that is essentially irrelevant - the front brake fixie is fully road legal and there is no negligence involved in riding one.
So the front brake equipped fixie stops at 0.52g, and the stopping distances are 5.8m at 17mph and 6.4m at 18mph.
Now all that is probably assuming accuracy in figures and reporting which isn't justified, but it leaves him possibly stopping 25cm from the victim if he braked in the most efficient way possible. Not a lot of room for error in braking performance. I'm thinking that rather than braking his best option was to swerve...
As an aside, I've seen this being discussed on a few other cycling forums, and the most sensible discussion is certainly here - I think we're the only ones to appreciate the details of the law he is being prosecuted under.
don't forget about reaction time
Do forget it. Reference point is when he started swerving, not when he started thinking. Only one of those points can be determined from CCTV footage…
as epicsteve has noted as well though, even if you couldn't stop, with the refined data we have now it should be possible to calculate relatively easily and accurately what the speed (and hence relative kinetic energy) is of the cyclist as they hit the pedestrian.
And given the mass difference effect of the KE is far lower than say a car, being hit at say 5mph is 'broadly speaking' equivalent to being walked into whereas being hit by a car at 5 mph will still knock you right over.
That said - as in an earlier post I've sometimes accelerated to avoid hitting someone / something and it's not a thought process, it's instinct so i still don't see that a choice to swerve as opposed to brake is necessarily a decision that you can blame him for.
don't forget about reaction timeDo forget it. Reference point is when he started swerving, not when he started thinking. Only one of those points can be determined from CCTV footage…
I don't think it's necessarily that simple, but rather that the prosecution do want the jury to see the timeline/chain of events in very black and white terms, and to focus on the actions, times and distances that they have identified in the CCTV, and to accept the prosecution's assertions of what the defendant [i]should[/i] have done and [i]when[/i], and what the different outcome would have been as a result.
Consequently they have examined the CCTV footage and identified a particular point at which the defendant swerves, and have sought to reduce everything that happened to a simple binary view of the whole case: if the defendant had had brakes and used them at that point, the woman would still be alive, he didn't and swerved instead, she was killed, ergo it's manslaughter.
That may be a fair way - and possibly the only reasonable way - of presenting the prosecution case, and the jury may accept it and convict.
However, I think people's actions and thinking processes are a lot more complex and messier in a real life emergency. The defendant was not having to make decisions just about his own speed and direction, but also simultaneously watch the woman, who reportedly moved across the road and then back and stopped, and so consequently he was continually having to process her movements, and factor into his own decisions not only where she was at any given time, but also try to anticipate where she would be when he would draw level with her. This is something car drivers generally don't experience: their speeds are such that the HC can reduce them to simple thinking and braking time distances, as opposed to - in this case - woman steps into road to cross it, think, react; woman stops, think, react; woman steps back, think, react.
It's a big assumption that a competent cyclist, or any of us, would not have similarly swerved at that point rather than use brakes, and only concluded maybe a second or so [i]later[/i] that swerving was not going to prevent a collision and only then decide to brake instead. Equally many/most/all of us would probably have been reducing speed much earlier on (the defence barrister did put it to the police witness that the CCTV shows the defendent leg braking at some point). If anything, as an 18 year old, his reaction times are probably better than any of ours.
At the end of the day, reducing the whole case to that distance of 6.65m and the stopping distance with brakes, is probably essential to be able to make a prosecution case in a trial that only lasts a few days. From what I have read so far of the case and the comments on here, my own feeling is that it's just not sufficiently clear cut to support a manslaughter conviction: the prosecution seems (based on the reporting) to have failed to prove unequivocally that the bike would have stopped before the impact if fitted with a legal minimum front brake: I would ideally have wanted repeated testing with measurements all showing that such a bike could have stopped within 75%-80% of the distance, to leave no room for doubt. Bear in mind that in such an emergency situation a cyclist does not have the benefit of knowing what his precise braking distance will be, so it's difficult to say that a competent cyclist on a bike with brakes would have braked rather than swerved, even if subsequent testing [i]in controlled conditions[/i] confirms that only braking, not swerving, would have prevented the collision. So I agree with aracer's earlier assessment that the direct connection between the unlawful act of no brake and the death appears not to have been proven. But I'm not on the jury and have not heard the evidence first hand.
Oh, I agree. I don't think a full-power emergency stop is what all, maybe even most, riders would do as their first reaction. I posted something relatively lengthy about that but I think it was on the Cycling UK forum thread, I think including a similar point about the prosecution argument appearing to be over-simplistic on that basis.
Either way, though, the initial response time is accounted for prior to the 6.65-9.65m given in the reports.
[quote=slowster ]It's a big assumption that a competent cyclist, or any of us, would not have similarly swerved at that point rather than use brakes, and only concluded maybe a second or so later that swerving was not going to prevent a collision and only then decide to brake instead.
From the available information I reckon I'd have swerved rather than braked, or at least the 18yo me would have (I did have an incident in my early 20s when I hurt myself quite badly having come off after swerving to avoid a pedestrian who'd stepped off the pavement, which led me to think I was better off just aiming at the pedestrian!) Hence unless there's other pertinent information which hasn't been reported, or viewing the CCTV resulted in me assessing the situation significantly differently I reckon I'd have to find him not guilty of manslaughter (probably also not guilty of W&F). That's on the basis that the prosecution is going for unlawful act manslaughter and that there is reasonable doubt on the direct link between the lack of brakes and the death (TBH I'm not sure it's even proven on balance of probabilities).
I still think it's irresponsible riding on the road without a front brake, and I still think he's a bit of an arse, but there's a good chance even if he had been on a road legal bike the collision would still have happened and the pedestrian would still have died.
[quote=slowster ]It's a big assumption that a competent cyclist, or any of us, would not have similarly swerved at that point rather than use brakes, and only concluded maybe a second or so later that swerving was not going to prevent a collision and only then decide to brake instead.
From the available information I reckon I'd have swerved rather than braked, or at least the 18yo me would have (I did have an incident in my early 20s when I hurt myself quite badly having come off after swerving to avoid a pedestrian who'd stepped off the pavement, which led me to think I was better off just aiming at the pedestrian!) Hence unless there's other pertinent information which hasn't been reported, or viewing the CCTV resulted in me assessing the situation significantly differently I reckon I'd have to find him not guilty of manslaughter (probably also not guilty of W&F). That's on the basis that the prosecution is going for unlawful act manslaughter and that there is reasonable doubt on the direct link between the lack of brakes and the death (TBH I'm not sure it's even proven on balance of probabilities).
I still think it's irresponsible riding on the road without a front brake, and I still think he's a bit of an arse, but there's a good chance even if he had been on a road legal bike the collision would still have happened and the pedestrian would still have died.
[quote=slowster ]It's a big assumption that a competent cyclist, or any of us, would not have similarly swerved at that point rather than use brakes, and only concluded maybe a second or so later that swerving was not going to prevent a collision and only then decide to brake instead.
From the available information I reckon I'd have swerved rather than braked, or at least the 18yo me would have (I did have an incident in my early 20s when I hurt myself quite badly having come off after swerving to avoid a pedestrian who'd stepped off the pavement, which led me to think I was better off just aiming at the pedestrian!) Hence unless there's other pertinent information which hasn't been reported, or viewing the CCTV resulted in me assessing the situation significantly differently I reckon I'd have to find him not guilty of manslaughter (probably also not guilty of W&F). That's on the basis that the prosecution is going for unlawful act manslaughter and that there is reasonable doubt on the direct link between the lack of brakes and the death (TBH I'm not sure it's even proven on balance of probabilities).
I still think it's irresponsible riding on the road without a front brake, and I still think he's a bit of an arse, but there's a good chance even if he had been on a road legal bike the collision would still have happened and the pedestrian would still have died.
[quote=slowster ]It's a big assumption that a competent cyclist, or any of us, would not have similarly swerved at that point rather than use brakes, and only concluded maybe a second or so later that swerving was not going to prevent a collision and only then decide to brake instead.
From the available information I reckon I'd have swerved rather than braked, or at least the 18yo me would have (I did have an incident in my early 20s when I hurt myself quite badly having come off after swerving to avoid a pedestrian who'd stepped off the pavement, which led me to think I was better off just aiming at the pedestrian!) Hence unless there's other pertinent information which hasn't been reported, or viewing the CCTV resulted in me assessing the situation significantly differently I reckon I'd have to find him not guilty of manslaughter (probably also not guilty of W&F). That's on the basis that the prosecution is going for unlawful act manslaughter and that there is reasonable doubt on the direct link between the lack of brakes and the death (TBH I'm not sure it's even proven on balance of probabilities).
I still think it's irresponsible riding on the road without a front brake, and I still think he's a bit of an arse, but there's a good chance even if he had been on a road legal bike the collision would still have happened and the pedestrian would still have died.
[quote=slowster ]It's a big assumption that a competent cyclist, or any of us, would not have similarly swerved at that point rather than use brakes, and only concluded maybe a second or so later that swerving was not going to prevent a collision and only then decide to brake instead.
From the available information I reckon I'd have swerved rather than braked, or at least the 18yo me would have (I did have an incident in my early 20s when I hurt myself quite badly having come off after swerving to avoid a pedestrian who'd stepped off the pavement, which led me to think I was better off just aiming at the pedestrian!) Hence unless there's other pertinent information which hasn't been reported, or viewing the CCTV resulted in me assessing the situation significantly differently I reckon I'd have to find him not guilty of manslaughter (probably also not guilty of W&F). That's on the basis that the prosecution is going for unlawful act manslaughter and that there is reasonable doubt on the direct link between the lack of brakes and the death (TBH I'm not sure it's even proven on balance of probabilities).
I still think it's irresponsible riding on the road without a front brake, and I still think he's a bit of an arse, but there's a good chance even if he had been on a road legal bike the collision would still have happened and the pedestrian would still have died.
My view: Do I think the lack of front brake was a factor in the accident? Yes. No I think he'll be convicted of manslaughter or "wanton on furious"? Probably not.
I'd really have to see the CCTV footage before I formed a definitive opinion.
I also thing that him being the type of rider who'd ride a track bike in London just to look cool (i.e. a pr1ck) is potentially as big a factor e.g. someone willing to make any kind of comment implying "she deserved it" is also the sort of person that might deliberately try and do a close fly-by at speed to frighten her because he thought she deserved that. I've certainly seen cyclists do that in London (and even in cases where they didn't have right of way, such as going between people on zebra crossings) and usually it'll be some posing fixie riding hipster.
Some quotes from the trial:
The cyclist also said: “F me and my health, I can heal and recover. The bike cannot. Thankfully I was going quite a slowish/moderate speed. Plus I skidded too, which slowed me down a bit.
He later wrote on an internet forum for fixed bike enthusiasts, how he twice warned Mrs Briggs to “get the f outta my way,” jurors were told earlier in the trial.
“But unfortunately the momentum kept me going. If I were going any faster the frame would have cracked or been shattered.”
The cyclist told cops after he was arrested: “I have slowed down enough for her to get past me”, jurors were told.
The court was told he had shouted twice after spotting Kim to “make her aware of his presence”.
I think we're expecting a verdict today. I'm 50:50 on whether he'll be convicted, however if by his own admission he locked up the back wheel then that suggest to me that braking was a factor and might also do so to the jury.
[quote=epicsteve ]however if by his own admission he locked up the back wheel then that suggest to me that braking was a factor and might also do so to the jury.
Ah, I'd missed that bit - however “I have slowed down enough for her to get past me” seems quite useful for the defence case.
however “I have slowed down enough for her to get past me” seems quite useful for the defence case.
Yes, I guess it could be used to say "I deliberately didn't come to a stop because there was a 'safe' route for me behind her, so the brakes on the bike are irrelevant because I wouldn't have been using them whether I had 0,1 or 2 brakes". Which puts the collision into 'momentary lapse' territory rather than a pre-meditated decision to take a 'dangerous' 'racing/track bike' onto the road.
Does anyone know if the 6.65m gap when he started swerving is when he swerved to go behind her or a second movement when he realised she was moving backwards, into his path, and he was trying to avoid a collision?
I think he'll be found guilty of manslaughter and W&F btw, which will grate because of the comparison to drivers who [s]kill[/s] are behind the wheel when pedestrians are fatally 'in collision' with their cars.
He took a vehicle on the road that was not road legal. That is the sole reason he is being charged with manslaughter. If a driver took a track car on the road and killed someone they'd also be charged with manslaughter.
Taking a vehicle on the road which is not road legal is not the same in the eyes of the law as taking an unroadworthy vehicle on the road.
[quote=avdave2 ]Taking a vehicle on the road which is not road legal is not the same in the eyes of the law as taking an unroadworthy vehicle on the road.
Both are a failure to comply with construction and use regulations, so no, legally there is no difference (there's nothing particularly special legally about not having a front brake, as mentioned earlier it's not fundamentally legally different to having a bald tyre).
He took a vehicle on the road that was not road legal. That is the sole reason he is being charged with manslaughter. If a driver took a track car on the road and killed someone they'd also be charged with manslaughter.
I was talking about the (as yet, unknown) [i]verdict [/i]not the [i]charge[/i]. And that's what all of the debate is about, nobody seems to disagree with the charge. It's about the link between the brakes and the death.
And that's what all of the debate is about, nobody seems to disagree with the charge.
There were definitely grounds for charging him IMHO. Still not sure one way or the other on the verdict (or even on what the verdict should be) given I haven't seen the most crucial evidence which is the CCTV footage.
not fundamentally legally different to having a bald tyre).
But if you had deliberately made said tyre bald, told people about it and THEN gone out for a drive.....
But if you had deliberately made said tyre bald, told people about it and THEN gone out for a drive.....
It's more like someone fitting racing slicks to a road car 'cause they thought they looked cooler then killing a pedestrian who stepped out in front of them in the wet, in conditions that were proved as being possible to stop from in a car with road tyres but not one with slicks. Suspect that'd get a manslaughter charge (and probably a conviction).
But if you had deliberately made said tyre bald, told people about it and THEN gone out for a drive.....
Then any charges (beyond the simple one for driving with bald tyres) would depend on whether the collision was caused/affected by the tyres.
E.g. if you get out of the car and forget to put the handbrake on, it rolls down a hill and squashes someone. The condition of the tyres is irrelevant to the squashing.
Or like the driver who hit the black ice and wiped out a group of cyclists.